Regenerative braking systems capture, and possibly store for future use, at least part of the kinetic energy lost by a vehicle as it brakes. Such systems are often employed by electric and hybrid vehicles. When a regenerative brake is applied, an electric drive motor of the vehicle acts as a generator and converts the vehicle's kinetic energy into electrical energy, which is used to charge the battery. However, when the battery is at full capacity, such a system cannot be used and therefore vehicles with regenerative braking systems are also provided with conventional friction brakes.
Hybrid vehicles tend to be significantly heavier than other vehicles since they comprise a greater number of component parts. As such, they tend to have correspondingly larger friction brakes to ensure that the friction brakes can stop the vehicle sufficiently quickly. In turn, this further increases the mass of such vehicles relative to conventional vehicles. However, it is generally desired to reduce the mass of vehicles, particularly their un-sprung mass.
JP6113404 discloses an arrangement where energy recovered by a regenerative braking system is used to drive brake cooling fans for friction brakes. This enables regenerative braking to be employed even when the vehicle battery is fully charged and, by cooling the friction brakes, improves their fade resistance. Power generated during regenerative braking is apportioned between the vehicle battery and brake cooling fans depending on the state of charge of the battery. So, when the battery is not fully charged a greater proportion of the recovered energy is directed to the battery. When the battery is fully, or nearly fully, charged a greater proportion of the energy is directed to the cooling fans. This provides a crude measure of control in that greater brake cooling is afforded when the battery is fully charged when regenerative braking is limited and so greater reliance is placed on the friction brakes causing them to generate more heat which must be dissipated.
However, this arrangement still causes unnecessary operation of the brake cooling fans leading to wasted energy and/or inefficient operation of the mechanical brakes.
It is an object of embodiments of the present invention to at least partially overcome these problems.